Random Access in Encoded Full Parallax Light Field Images

ABSTRACT

Methods and systems for light field image encoding and decoding are disclosed. According to some embodiments, the method receives scene metadata and input light field images associated with a scene. The method further performs a first encoding operation on the scene metadata and the input light field images to generate reference views and reference disparity information. The method further performs a second encoding operation based on the reference views, the reference disparity information, and synthesized residuals to output encoded light field data, where the encoded light field data comprises encoded reference views, encoded reference disparity information, and encoded synthesized residuals. The method further randomly accesses and selects a group of reference views and corresponding disparity information from the encoded light field data based on one or more selected regions of interest. And the method transmits the selected group of reference views, the selected corresponding disparity information, and the encoded synthesized residuals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/690,001 filed on Jun. 26, 2018, the disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

Embodiments of the invention relate to image and video compression. Morespecifically, embodiments of the invention relate to random access inencoded full parallax light field images.

BACKGROUND

Depth perception in the human visual system (HVS) relies on severaldepth cues. These cues can be categorized as either psychological (e.g.,perspective, shading, lighting, relative size, occlusion and texturegradient, etc.) or physiological depth cues (e.g., vergence,accommodation, motion parallax, binocular disparity, etc.). Whilepsychological depth cues provide a relative understanding of the depthin a light field, physiological depth cues provide absolute depthinformation. Commercially available three-dimensional (3D) displaysoften use a subset of the physiological depth cues to enhance the lightfield viewing experience.

Glasses-based 3D displays have been gaining popularity since theintroduction of glasses-based 3D televisions (TVs) sold by all major TVmanufacturers. A shortcoming of the currently available technology isparadoxically the actual use of 3D glasses, which glasses can becategorized as either active or passive. In general, glasses-basedtechnology is known to be uncomfortable for viewers to use for long timeperiods and poses challenges for people who require prescriptionglasses.

Existing autostereoscopic displays use directional modulators (such asparallax barriers or lenticular sheets) attached to a display surface tocreate a 3D effect without requiring glasses. Commercially availableautostereoscopic displays typically use horizontal parallax to present3D information to the viewer. Deficiencies of this form of displaytechnology include a limited viewing angle and a limited resolution perview, each of which results in a lower quality 3D image. In addition,within the viewing angle of such displays, the user is required to keephis or her head vertical. Otherwise, the 3D effect would disappear.

Long viewing times in both glasses-based 3D displays and in horizontalparallax-only light field displays typically cause discomfort due to aphysiological effect known as “vergence accommodation conflict” (VAC).See, e.g., Hoffman, D., Girshick, A., Akeley, K. & Banks, M. (2008),“Vergence-accommodation conflicts hinder visual performance and causevisual fatigue”, Journal of Vision 8 (3), 33. VAC is caused by the factthe viewer's eyes are focused on the display surface plane but also needto converge away from it in order to perceive objects that are depictedat different depths, and thus viewer discomfort occurs.

A more natural 3D effect is achieved using full parallax 3D displaytechnology. In addition to horizontal parallax, full parallax 3D displaytechnology includes vertical parallax such that a vertical movement ofthe viewer provides a different view of the 3D scene. Full parallaxdisplays generally have an order of magnitude or more views thanhorizontal parallax-only displays. Arranging these views densely createsa very natural 3D image that does not change when a user moves or tiltshis or her head, and also eliminates VAC by providing correctaccommodation and vergence cues. 3D displays that eliminate the VAC maybe referred to as “VAC-free” 3D displays.

The main challenge associated with the aforementioned full parallax 3Ddisplays is that the increase in modulated image resolution required torender full parallax 3D images with wide viewing angles creates a newimpairment for the display system, namely, a dramatically increasedamount of image data. The generation, acquisition, transmission andmodulation (or display) of very large image data sets required for aVAC-free full parallax light field display requires a data rate in thetens of terabits per second (Tbps).

A brief inspection of light field input images shows the ample inherentcorrelation between the light field data elements (known as holographicelements or “hogels”) and compression algorithms that have been proposedto deal with this type of data in the prior art. See, e.g., M. Lucente,“Diffraction-Specific Fringe Computation for Electro-Holography”,Doctoral Thesis Dissertation, MIT Depart. of Electrical Engineering andComputer Science, September 1994. However, as can be appreciated bythose skilled in the art, only a limited number of the compressionmethods described in the prior art can practically be implemented inreal-time and none of these methods can render and/or compress theamount of data required to drive a full parallax VAC-free display inreal-time.

For example, currently, the most advanced video compression format,H.264/AVC, can compress ultra-high resolution video frames (4,096×2,304@ 56.3, or 0.5 Gpixels/sec.) at a data bit rate of approximately 3Gbits/sec. See, e.g., ISO/IEC 14496-10:2003, “Coding of AudiovisualObjects—Part 10: Advanced Video Coding,” 2003, also ITU-T RecommendationH.264 “Advanced video coding for generic audiovisual services”. H264/AVCfails to achieve sufficient compression needed for the useabletransmission of light field image data, much less if the light field isrefreshed in real time at a 60 Hz video rate where data rates can reachup to 86 Tbps.

Current compression standards do not exploit the high correlation thatexists both in horizontal and vertical directions in a full parallaxlight field image. New compression standards targeting 3D displays arebeing developed. Nevertheless, they are targeting horizontal parallaxonly, a limited number of views, and usually require an increased amountof memory and related computational resources. Compression algorithmsmust balance image quality, compression ratio and computational load. Asa general rule, a higher compression ratio in an encoder increases thecomputational load, making real-time implementation difficult. If bothhigh compression and decreased computational load is required, thenimage quality is sacrificed. A compression solution that is able tosimultaneously provide high image quality, a high compression ratio andrelatively low computational load is highly desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 illustrates a light field imaging system according to oneembodiment.

FIG. 2 is a flow diagram illustrating a method of light field encodingaccording to one embodiment.

FIG. 3 is a flow diagram illustrating a method of light field decodingaccording to one embodiment.

FIG. 4 is a block diagram illustrating an example of light fieldencoding and decoding architecture according to one embodiment.

FIG. 5 is a block diagram illustrating different components in encodedlight field data.

FIG. 6 is a block diagram illustrating an exemplary technique forselecting reference views associated with a region of interest (RoI)according to one embodiment.

FIG. 7 is a block diagram illustrating an exemplary technique forselecting reference views associated with multiple ROIs according to oneembodiment.

FIG. 8 is a flow diagram of an MR-DIBR operation according to oneembodiment.

FIG. 9 is a block diagram illustrating a representation of perspectivereference views and orthographic reference views.

FIG. 10 is a block diagram of a data processing system, which may beused with one embodiment.

DETAILED DESCRIPTION

Various embodiments and aspects of the inventions will be described withreference to details discussed below, and the accompanying drawings willillustrate the various embodiments. The following description anddrawings are illustrative of the invention and are not to be construedas limiting the invention. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentinvention. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present inventions.

Reference in the specification to “one embodiment”, “an embodiment” or“some embodiments” means that a particular feature, structure, orcharacteristic described in conjunction with the embodiment can beincluded in at least one embodiment of the invention. The appearances ofthe phrase “in one embodiment” in various places in the specification donot necessarily all refer to the same embodiment.

Aspects of the invention herein introduce light field compressionmethods that overcome the drawbacks of the prior art, thereby making itfeasible to create VAC-free full parallax 3D displays that utilize thecompression methods of this invention for compressed light field imagingsystems to reduce the required data rate, the processing requirements inboth encoding and decoding and also power consumption for the entireimaging system. Additional advantages of the invention will becomeapparent from the following detailed description of various embodimentsthereof that proceeds with reference to the accompanying drawings.

As is known, the transmission of large data sets can be facilitated withthe use of a compressed data format. In conventional light fieldsystems, the entire light field is first captured, and then it iscompressed (or encoded) using either conventional image/videocompression algorithms or light-field specific encoders. The compresseddata can then be transmitted, stored and/or reconditioned for the lightfield display, where it is decompressed (or decoded) and modulated(examples of prior art light field compression systems are disclosed in,for instance, U.S. Pat. No. 8,401,316 B2, and U.S. Publication No.US2013/0077880).

Light fields can be compressed using a multi-view compression (MVC)standard. See, e.g., A. Vetro, T. Wiegand, G. Sullivan, “Overview of thestereo and multiview video coding extensions of the H.264/MPEG-4 AVCstandard”, Proceedings of the IEEE, vol. 99, no. 4, Apr. 2011. Using theMVC standard, the hogels are interpreted as frames of a multi-viewsequence and the disparity between images is estimated and encoded. Theblock-based disparity estimation generates inaccuracies that are encodedby a block-based encoder, and the compression performance grows linearlywith the number of images.

To improve multi-view coding, new coding standards are considering theadoption of techniques from the field of computer vision. See, e.g.,ISO/IEC JTC1/SC29/WG11, Call for Proposals on 3D Video CodingTechnology, Geneva, Switzerland, March 2011. With the use of per-pixeldepth information, reference images can be projected to new views andthe synthesized images can be used instead of the costly transmission ofnew images. This technique requires increased computational resourcesand local memory on the decoder side, posing a challenge for itsreal-time implementation. Prior art compression tools are also targetingtheir use in horizontal-only multiview sequences and do not exploit thegeometric arrangement of integral images.

Methods developed exclusively for light field image compression includea vector quantization method described by Levoy et al., “Light FieldRendering”, Computer Graphics, SIGGRAPH 96 Proceedings, pp. 31-42, 1996,and video compression-based methods described by Magnor et al., “DataCompression for Light-Field Rendering”, IEEE Transaction on Circuits andSystems for Video Technology, v. 10, n. 3, April 2000, pp. 338-343. Theuse of vector quantization is limited and cannot achieve highcompression performances such as those presented by Magnor et al., whichmethods are similar to a multiview compression algorithm where thegeometrical regularity of the images is exploited for disparityestimation. However, these methods require an increased amount of localmemory and are not well-suited for real-time implementation.

Along with the problem of image data compression, there is a relatedissue of image data acquisition. The generation of the entire lightfield for encoding requires large amounts of processing throughput andmemory, and many samples may be discarded at the compression stage. Arecently developed technique referred to as “Compressed Sensing” (CS)attempts to address this problem. The underlying principal behindCompressive Sensing is that a signal that is highly compressible (orequivalently sparse) in some transform domains can be minimally sampledusing an incoherent basis and still be reconstructed with acceptablequality. See, e.g., Candès, E., Romberg, J., Tao, T., “Robustuncertainty principles: Exact signal reconstruction from highlyincomplete frequency information”, IEEE Trans. Inform. Theory 52 (2006)489-509. See also, e.g., David Donoho, “Compressed sensing,” IEEETransactions on Information Theory, Volume 52, Issue 4, April 2006,Pages: 1289-1306.

This new paradigm shifts the complexity from the acquisition to thereconstruction process, which results in the need for more complexdecoders. This tendency is aligned with the trend of computationaldisplays which present computational capability directly in the displaydevices. Displays that have computational capacity and are able to dealdirectly with compressed image data are known to those skilled in theart of image processing and light field technology as “compressivedisplays”. See, e.g., Gordon Wetzstein, G., Lanman, D., Hirsch, M.,Heidrich, W., and Raskar, R., “Compressive Light Field Displays”, IEEEComputer Graphics and Applications, Volume 32, Issue 5, Pages: 6-11,2012; Heide, F., Wetzstein, G., Raskar, R. and Heidrich, W., “AdaptiveImage Synthesis for Compressive Displays”, Proc. of SIGGRAPH 2013 (ACMTransactions on Graphics 32, 4), 2013. See also, e.g., S. Guncer, U.S.Publication No. US2010/0007804, Image Construction Method Based VideoDisplay System, Jan. 14, 2010; S. Guncer, U.S. Patent Publication No.US2010/0225679, Multi-Pixel Addressing Method for Video Display System,Sep. 9, 2010.

In Graziosi et al., “Depth assisted compression of full parallax lightfields”, IS&T/SPIE Electronic Imaging. International Society for Opticsand Photonics (Mar. 17, 2015), a synthesis method that targets lightfields and uses both horizontal and vertical information was introduced.The above method adopts aspects of a method called Multiple ReferenceDepth-Image Based Rendering (MR-DIBR) and utilizes multiple referenceswith associated disparities to render the light field. In this approach,disparities are first forward warped to a target position. Next, afiltering method is applied to the warped disparities to mitigateartifacts such as cracks caused by inaccurate pixel displacement. Thethird step is the merging of all of the filtered warped disparities.Pixels with smaller depths (i.e., those closest to the viewer) areselected. Finally, the merged elemental image disparity is used tobackward warp the color from the references' colors and to generate thefinal synthesized elemental image.

Prior art light field compression methods using depth image-basedrendering (DIBR), while efficient for compression of elemental images,are unable to incorporate occlusion and hole-filling functions necessaryto provide high quality light field images at acceptable compressionratios. An example of such a prior art DIBR compression method isdisclosed in, for instance, U.S. Publication No. 2016/0360177 entitled,“Methods for Full Parallax Compressed Light Field Synthesis UtilizingDepth Information”, the entire contents of which are incorporated hereinby reference.

As detailed in U.S. Publication No. 2016/0021355, “Preprocessor for FullParallax Light Field Compression”, the disclosure of which areincorporated herein by reference, MR-DIBR enables the reconstruction ofother perspectives from reference images and from reference disparitymaps. Reference images and reference disparity maps are initiallyselected via a “visibility test” in one embodiment. The visibility testmakes use of: 1) the distance of the objects from the modulationsurface, and 2) the display's field of view (“FOV”), to determine anddefine the reference images and disparity maps used by the method.

In general, a scene that contains objects that are farther from themodulation surface tends to result in a smaller number of referenceimages and reference disparity maps as compared to a scene that containsobjects that are closer to the modulation surface. Smaller numbers ofreference images and reference disparity maps result in a highercompression ratio. In general, however, higher compression ratios alsomean greater degradation in the decoded image.

Accordingly, the prior art fails to adequately address the need for highcompression ratio, high quality, low computational load light field datacompression as is required for practical implementation of VAC-free fullparallax, and wide viewing angle 3D display technologies.

Aspects of the invention improve upon a method of light field encodingor compression, for example, by using random access with MR-DIBR. Thegeneral concept is to further compress the output (i.e., referenceinformation) of the MR-DIBR method (e.g., reference views and referencedisparity maps) as well as the residuals of synthesized views(collectively as encoded light field data) using image/video compressionmethods, such as JPEG 2000. Based on a particular region of interest(RoI), the random access approach would enable selection of referenceviews and corresponding disparity maps associated with the RoI from theencoded light field data (along with the residuals) to decode ordecompress.

According to one aspect, the method of light field image encoding isdescribed. The method receives scene metadata and input light fieldimages associated with a scene. The method further performs a firstencoding operation on the scene metadata and the input light fieldimages to generate reference views and reference disparity information.The method further performs a second encoding operation based on thereference views, the reference disparity information, and synthesizedresiduals to output encoded light field data, where the encoded lightfield data comprises encoded reference views, encoded referencedisparity information, and encoded synthesized residuals. The methodfurther randomly accesses and selects a group of reference views andcorresponding disparity information from the encoded light field databased on one or more selected regions of interest. And the methodtransmits the selected group of reference views, the selectedcorresponding disparity information, and the encoded synthesizedresiduals.

According to another aspect, a method of light field image decoding isdescribed. The method receives a selected group of reference views,selected corresponding disparity information, and encoded synthesizedresiduals associated with one or more regions of interest. The methodfurther performs a first decoding operation on the selected group ofreference views, the selected corresponding disparity information, andthe encoded synthesized residuals to output decoded reference views,decoded disparity information, and decoded synthesized residuals. Themethod further performs a second decoded operation on the decodedreference views and the decoded disparity information to generatesynthesized views. And the method generates decoded light field databased on the synthesized views and the decoded synthesized residuals.

FIG. 1 illustrates a light field imaging system according to oneembodiment. Referring to FIG. 1, light field imaging system 100 mayinclude a capturing system 103 and a light field display system 107 thatmay be communicatively coupled to each other, for example, over anetwork (not shown), such as the Internet or cloud service. Capturingsystem 103 may include a capturing device (not shown) such as alight-field camera, action camera, animation camera, camcorder, cameraphone, compact camera, digital camera, high-speed camera, mirrorlesscamera, or pinhole camera. In one embodiment, capturing system 103includes, but is not limited to, pre-processing engine 105 (alsoreferred to as pre-processing logic, pre-processing module, orpre-processing unit, which may be implemented in software, hardware, ora combination thereof) and compression logic 109 (also referred to ascompression engine, compression module, or compression unit, which maybe implemented in software, hardware, or a combination thereof).

Pre-processing engine 105 may capture, acquire, receive, create, format,store and/or provide light field input data (or scene/3D data) 101,which may represent an object or a scene, to be utilized at differentstages of a compression operation (as discussed in more detail hereinbelow). To do so, pre-processing engine 105 may generate a priori (orpre-processing) information associated with light field input data 101,for example object locations in the scene, bounding boxes, camera sensorinformation, target display information and/or motion vectorinformation. Moreover, in some embodiments, pre-processing engine 105may perform stereo matching and/or depth estimation on the light fieldinput data 101 to obtain a representation of the spatial structure of ascene, for example one or more depth maps (or disparity maps) and/orsubimages (or subaperture images) associated with the object or scene.

In one embodiment, pre-processing engine 105 may convert the light fieldinput data 101 from data space to display space of light field displaydevice 111. Conversion of the light field input data 101 from data spaceto display space may be needed for the light field display device 111 toshow light field information in compliance with light field displaycharacteristics and the user (viewer) preferences. When the light fieldinput data 101 is based on camera input, for example, the light fieldcapture space (or coordinates) and the camera space (or coordinates) aretypically not the same, and as such, the pre-processing engine 105 mayneed to convert the data from any camera's (capture) data space to thedisplay space. This is particularly the case when multiple cameras areused to capture the light field and only a portion of the captured lightfield in included in the viewer preference space. This data space todisplay space conversion is done by the pre-processing engine 105 byanalyzing the characteristics of the light field display device 111 and,in some embodiments, the user (viewer) preferences. Characteristics ofthe light field display device 111 may include, but are not limited to,image processing capabilities, refresh rate, number of hogels andanglets, color gamut, and brightness. Viewer preferences may include,but are not limited to, object viewing preferences, interactionpreferences, and display preferences.

In one embodiment, pre-processing engine 105 may take the displaycharacteristics and the user preferences into account and convert thelight field input data 101 from data space to display space. Forexample, if the light field input data 101 includes mesh objects, thenpre-processing engine 105 may analyze the display characteristics (suchas number of hogels, number of anglets, and FOV), analyze the userpreferences (such as object placement and viewing preferences),calculate bounding boxes, motion vectors, etc., and report suchinformation to the light field display system 107. In one embodiment,data space to display space conversion may include data formatconversion and motion analysis in addition to coordinate transformation.In one embodiment, data space to display space conversion may involvetaking into account the position of the light modulation surface(display surface) of the light field display device 111, and theobject's position relative to the display surface.

Encoding (or compression) logic 109 may receive the a priori (orpre-processing) information from pre-processing engine 105 forcompression. For example, encoding logic 109 may execute one or morecompression methods at different stages using the a priori informationin order to generate compressed information (e.g., reference and/orresidual information). In one embodiment, the compression methods may bebased on image-based rendering (IBR), depth image-based rendering(DIBR), and/or multiple-reference depth image-based rendering (MR-DIBR).In one embodiment, the compression methods may, additionally oralternatively, be based on one or more image compression standards suchas Joint Photographic Experts Group (JPEG), JPEG 2000, JPEG XS, or videocompression standards (also referred to as video compression methods,video compression algorithms, or video compression codecs), such asMoving Picture Experts Group (MPEG), H.264, High Efficiency Video Coding(HEVC), Theora, RealVideo, RV40, VP9, AV1, Audio Video Interleaved(AVI), Flash Video (FLV), RealMedia, Ogg, QuickTime, and/or Matroska.Encoding logic 109 may then communicate the encoded or compressedinformation, for example over a network (not shown), such as theInternet or cloud service, to decoding (or decompression) logic 113 toperform decompression operations. In one embodiment, the compressedinformation may be stored in a storage device (not shown) to beretrieved (or loaded) by decoding logic 113. The storage device, forexample, may be a hard disk drive (HDD), solid state device (SSD), readonly memory (ROM), random access memory (RAM), or optical storage media.

As further shown in FIG. 1, light field display system 107 may include,but is not limited to, decoding logic 113 (also referred to as decodingengine, decoding module, or decoding unit, which may be implemented insoftware, hardware, or a combination thereof) and light field displaydevice 111 communicatively coupled to each other. The light fielddisplay device 111 may be any type of light field display device, suchas a glasses-based 3D display device, autostereoscopic display device,VAC display device, or VAC-free full parallax 3D display device. Asshown, light field display device 111 may include, but is not limitedto, display logic 115 (also referred to as display engine, displaymodule, or display unit, which may be implemented in software, hardware,or a combination thereof).

In one embodiment, decoding logic 113 may execute one or more decodingor decompression methods on the encoded information, which may beretrieved from the storage device, in order to generate decodedinformation (e.g., reference and/or residual information). Additionallyor alternatively, decoding logic 113 may further decode some of thedecoded information (e.g., reference information) to produce synthesizedimages (e.g., elemental images or hogel images). Using the synthesizedimages and part of the decoded information (e.g., residual information),decoding logic 113 may reconstruct the original object or scenerepresented by light field input data 101. The reconstructed images ofthe object or scene may be transmitted to display logic 115 to display,modulate or render on light field display device 111. As with thecompression methods previously discussed, in one embodiment, the decodedoperations may be based on IBR, DIBR, and/or MR-DIBR. In one embodiment,the decoded operations may, additionally or alternatively, be based onone or more image compression standards such as JPEG, JPEG 2000, JPEGXS, or one or more video compression standards, such as MPEG, H.264,HEVC, Theora, RealVideo, RV40, VP9, AV1, AVI, FLV, RealMedia, Ogg,QuickTime, and/or Matroska.

It should be appreciated that while FIG. 1 shows the light fieldcapturing system 103 as being separate from the light field displaysystem 107, in some embodiments the light field capturing system 103 maybe part of the light field display system 107. It should also beappreciated that while FIG. 1 shows the pre-processing engine 105 aspart of the light field capturing device 103, in some embodiments thepre-processing engine 105 may be part of the light field display system107 or another system, logic, engine, module or unit. It should furtherbe appreciated that while FIG. 1 shows the encoding logic 109 as part ofthe capturing system 103, in some embodiments, encoding logic 109 may bepart of the light field display system 107 or another system, logic,engine, module or unit.

FIG. 2 is a flow diagram illustrating a method of light fieldcompression according to one embodiment of the invention. Process 200may be performed by processing logic that includes hardware (e.g.circuitry, dedicated logic, etc.), software (e.g., embodied on anon-transitory computer readable medium), or a combination thereof. Forexample, process 200 may be performed by encoding logic 109 of FIG. 1.

Referring to FIG. 2, at block 201, the processing logic receivespre-processing information associated with light field input data 101.As previously described, pre-processing information may include objectlocations in the scene, bounding boxes, camera sensor information,target display information and/or motion vector information. In someembodiments, pre-processing information may include a representation ofthe spatial structure of a scene, for example one or more depth maps (ordisparity maps) and/or subimages (or subaperture images) associated withthe object or scene.

At block 202, the processing logic performs a first compressionoperation on the pre-processing information. For example, using depthmaps and/or subimages (or subaperture images) from the pre-processinginformation, one or more light field compression methods (e.g., IBR,DIBR, or MR-DIBR) may be performed to generate reference data 203. Thereference data 203 may include reference views (e.g., elemental imagesor hogel images) and corresponding reference disparity maps.

Because there remain significant similarities among the referenceelemental images in DIBR, for example, further compression is possibleto improve bandwidth efficiencies. The same logic also applies to thedisparity map operation. The elemental images and disparity maps fromdifferent spatial/angle locations can be rearranged in successivesequences and treated as temporal frames to be encoded by a video codec.

One of the biggest issues of any DIBR algorithm, however, is thegeneration of holes and cracks due to inaccuracy in depth values,round-off errors and object disocclusion. MR-DIBR reduces the holessignificantly due to using multiple references; however, synthesizedimages can still be different from the original images. The differencesbetween the original and estimated values of synthesized elementalimages are defined as residual images, which can also be encoded by avideo codec. By encoding the reference elemental images, disparity maps,and residual images with a video codec, the overall distortion can rangefrom lossy to lossless with corresponding bit rate tradeoffs infine-grained steps.

Accordingly, at block 204, the processing logic performs a secondcompression operation on the reference data and residual data, forexample residuals of synthesized views, such as synthesized elemental orhogel images. As previously described, one or more image compressionstandards such as JPEG, JPEG 2000, JPEG XS, or one or more videocompression standards, such as MPEG, H.264, HEVC, Theora, RealVideo,RV40, VP9, AV1, AVI, FLV, RealMedia, Ogg, QuickTime, and/or Matroska,may be executed to compress (or encode) the reference data and residualdata, thereby outputting encoded or compressed light field data 205,which includes compressed reference and residual data.

At block 206, one or more encoded reference views and correspondingdisparity maps may be selected from encoded light field data 205 (asdiscussed in more detailed herein below) based on an RoI. The RoI may berequested by a user. The selected encoded reference views andcorresponding reference disparity maps along with the encoded residualdata may be generated or outputted as encoded RoI data 207.

FIG. 3 is a flow diagram illustrating a method of light field decodingaccording to one embodiment. Process 300 may be performed by processinglogic that includes hardware (e.g. circuitry, dedicated logic, etc.),software (e.g., embodied on a non-transitory computer readable medium),or a combination thereof. For example, process 300 may be performed bydecoding logic 113 of FIG. 1.

Referring to FIG. 3, at block 301, the processing logic receives encodedRoI data. At block 302, the processing logic performs a firstdecompression operation on the encoded RoI data. For example, one ormore image decompression standards such as JPEG, JPEG 2000, JPEG XS, orone or more video decompression (or decoding) standards, such as MPEG,H.264, HEVC, Theora, RealVideo, RV40, VP9, AV1, AVI, FLV, RealMedia,Ogg, QuickTime, and/or Matroska, may be executed to decompress (ordecode) the encoded RoI data and output decoded reference dataassociated with the RoI, for example decoded reference views andcorresponding reference disparity maps associated with the RoI, andresidual data, for example residuals of synthesized views (as shown atblock 303). At block 304, the processing logic performs a seconddecompression operation on the decoded reference data. In oneembodiment, one or more light field decompression (or decoding) methods,such as IBR, DIBR or MR-DIBR, may be executed to produce or generatesynthesized views (as shown at block 305). At block 306, the processinglogic generates decoded light field data based on the synthesized viewsand decoded residual data. As an example, in one embodiment the residualdata may be added to the synthesized views to produce the decoded lightfield data, which may be modulated (or displayed) on a light fielddisplay device (e.g., light field display device 111 of FIG. 1).

FIG. 4 is a block diagram illustrating an example of light fieldencoding and decoding architecture according to one embodiment. In someembodiments, the architecture may be implemented as part of light fielddisplay system 107 of FIG. 1 (e.g., in encoding logic 109 and/ordecoding logic 113 of FIG. 1).

As shown in FIG. 4, the architecture (or codec) includes an encodingstage 400 and a decoding stage 450. Encoding stage 400 includes MR-DIBRencoder 403 and image/video encoder 408. MR-DIBR encoder 403 may receiveand compress camera (or scene) metadata 401 and input light field data402 in order to generate reference views 404 (which may be elementalimages (EIs) or hogels) and corresponding reference disparity maps 405.In one embodiment, metadata 401 may include optical characteristics of acapturing device and the captured data, such as camera pixel count,camera location(s), lens FOV, scene composition, its distance from thecamera(s), and/or display device characteristics.

Reference views 404, reference disparity maps 405, and synthesizedresiduals 407 (discussed in more detail herein below) may be provided toimage/video encoder 408 (e.g., JPEG, JPEG 2000, or JPEG XS encoder, orMPEG, H.264, HEVC, Theora, RealVideo, RV40, VP9, AV1, AVI, FLV,RealMedia, Ogg, QuickTime, or Matroska encoder) for further compression.For example, image/video encoder 408 may compress (or encode) thereference views 404, reference disparity maps 405 and synthesizedresiduals 407 at a bit rate in order to generate encoded light fielddata (e.g., compressed reference views, reference disparity maps, andsynthesized residuals). In one embodiment, image/video encoder 408 mayinclude multiple encoders (e.g., JPEG 2000 encoders) to encode thereference views 404, reference disparity maps 405 and synthesizedresiduals 407.

As further shown in FIG. 4, the encoded light field data is communicatedto a reference selection 410. Reference selection 410 provides randomaccess capability that can be measured by the following formula:

$\frac{{Resources}\mspace{14mu} {used}\mspace{14mu} {in}\mspace{14mu} {random}\mspace{14mu} {access}\mspace{14mu} {of}\mspace{14mu} {an}\mspace{14mu} {RoI}\mspace{14mu} {with}\mspace{14mu} {the}\mspace{14mu} {Codec}}{\begin{matrix}{{Resources}\mspace{14mu} {used}\mspace{14mu} {in}\mspace{14mu} {full}\mspace{14mu} {decoding}} \\{{of}\mspace{14mu} {the}\mspace{14mu} {data}\mspace{14mu} {with}\mspace{14mu} {the}\mspace{14mu} {same}\mspace{14mu} {Codec}}\end{matrix}}$

Generally, the definition of an RoI in a 2D image is usually as simpleas an image region. However, due to the volumetric nature of light fieldimages, and various use cases, the definition of an RoI is morecomplicated for a light field image.

In some embodiments, the use cases for light field images can beexamined in two different ways:

First is display based which is considered the visualization of andinteraction with the light field image. The display determines the sizeof the RoI and number of views to be decoded. For example, direct viewlight field display (e.g., television, PC monitor) can display a subsetof the light field (subset of the views, subset of the total field ofview (FOV), etc.). Six depth of field (DoF) interaction may be possiblewith light field image, and a full suite of rendering operations is notrequired, though remapping may be needed. Another example is near eyedisplay (e.g., glasses) which requires fewer views than the direct viewlight field display (e.g., 1+ views/eye). In this case, six DoFinteraction may also be possible with the light field image, butadditional rendering operations may be needed as compared to direct viewlight field display. Yet another example is 2D display which usuallydisplays only one view. In this case, three DoF interaction with thedata is possible, but a full suite of rendering operations may beneeded.

Second is rendering based (e.g., a location to focus in an image) whichconsiders various algorithmic methods (e.g., depth of field change,refocus, relighting, motion parallax, navigation, enhanced analysis andmanipulation, reference JPEG Pleno CfP) to make use of the light fieldimage. Depth of field change is the change in the depth of field aftercapture in a flexible way. Refocus is the change of focus as well as theability to refocus on object(s) of interest after capture. Relighting isthe change of lighting, including both number of sources and thedirection of lighting in an already captured or synthesized scene.Motion parallax is the change of viewing perspective from observer'sposition. Navigation is the ability to view a scene from differentpositions and directions with the ability to explore the scene by movinginside the scene. Enhanced analysis and manipulation is the facilitationof advanced analysis and manipulation of objects within a scene, such astheir segmentation, modification, and even removal or replacement bytaking into account richer information extracted from plenoptic datasuch as depth (either directly or indirectly).

To accomplish the foregoing use cases, referring now to FIG. 5,reference selection 410 may access different components in encoded lightfield data 500, such as: view 502, multiple neighboring views 501,multiple non-neighboring views (e.g., views 502 and 505), a specificpixel from all the views (e.g., pixel 504), a specific group of pixelsfrom a specific group of views (e.g., group of pixels 503), or all theviews (i.e., full decoding).

Referring now to FIG. 6, which is a block diagram illustrating anexemplary technique for selecting reference views associated with aregion of interest (RoI) according to one embodiment, MR-DIBR requiresencoding of selected reference views (RVs) and their correspondingdisparity maps using, for example, JPEG 2000. Random access with MR-DIBRhas two components: (1) random access to a group of RVs and disparitymaps required for RoI access, closest in view distance to the desiredRoI, with JPEG 2000, and (2) synthesis of the RoI with the MR-DIBRmethod.

For example, as shown in FIG. 6, encoded light field data 600 mayinclude a multiplicity of RVs. RoI 601 may be randomly selected by RoIselection 409 of FIG. 4. RoI selection 409 may select RoI 601 based on arequest from a user. In one embodiment, RoI 601 may be a specific viewor a whole region (as indicated in the shaded area of FIG. 6). Based onthe location of RoI 601, reference selection 410 may determine that RVs602 a-d (and their corresponding disparity maps) have the closest inview distance to the desired RoI 601. Thus, RVs 602 a-d are selected forRoI access of RoI 601. Moreover, additional views can be accessed forfree (as indicated by path 603), that is no additional resources arerequired, with RVs 602 a-d.

Turning now to FIG. 7, an additional RoI 703 may be selected by RoIselection 409. In this scenario, non-adjacent RoI view access requiresadding more RVs (e.g., RV 704). However, the number of RVs required foradditional RoI 703 is generally smaller than the number of RVs requiredfor the initial RoI 601 access as shown in FIG. 7. Also, additional RV705 can be accessed for free (i.e., no additional resources required)with new RV 704.

Accessing a single pixel or group of pixels from all the views requiresdecoding of all the RVs. However synthesis of the RoI does not requirethe synthesis of the whole intermediate view (IV). Instead both backwardwarping and forward warping operations can be simplified greatly due tosmaller number of pixels needed for warping.

FIG. 8 is a flow diagram of an MR-DIBR operation according to oneembodiment. At block 801, forward warping is performed for each of thereference disparities or disparity maps associated with an RoI (e.g.,RoI 601 or RoI 703). At block 802, disparity filtering is applied (e.g.,crack filter) in each of the forward warped reference disparity. Atblock 803, the forward warped and filtered disparity maps are mergedinto a reference disparity (e.g., synthesized depth). At block 804,backward warping is performed using the merged reference disparity andreference views to produce synthesized views (or texture).

In some embodiments, the MR-DIBR operation is performed by processinglogic which may include software, hardware, or a combination thereof. Inone embodiment, the use of multiple references increases the chance thatthe disoccluded texture after warping will be present in one of thereference disparities, and therefore hole filling is minimized orcompletely avoided. This provides a better quality than synthetichole-filling algorithms. However, it requires a careful selection of thereference elemental images while increasing MR-DIBR processing time andmemory usage.

In forward warping 801, the reference disparities may be shiftedaccording to the distance between the target image and the referenceimage, and their respective disparity values. In order to reduce thememory usage of multiple references, only the disparity is used forforward warping. Due to round-off and quantization errors, cracks mayappear in the forward warped disparity. Hence, disparity filtering 802may be used to detect the erroneous disparity values and correct themwith neighboring disparities. The warped and filtered disparities arethen merged together (at block 803), and since multiple references areused, there is a probability that the disoccluded view will be presentin one of the references. Finally, in backward warping 804 the mergeddisparity is used to indicate the location in the reference images toobtain the final texture.

With reference to FIG. 9, accessing a single pixel or group of pixels(e.g., pixels 901-904) from all the views can be handled by decoding asingle view (e.g., view 910) if both angular and spatial reference viewsare encoded. In light field images, there is generally a one to onemapping between angular representation and spatial representation. Aview in one representation belongs to multiple views as a single pixelin another representation.

These representations are usually perspective pictures and orthographicpictures. Therefore if one encodes perspective reference views as wellas orthographic reference views. Then both spatial and angularrepresentations can be accessed by just decoding a single view. Themethods for encoding and decoding perspective and orthographic views isdisclosed in U.S. patent application Ser. No. 15/993,268, entitled“Methods and Systems for Light Field Compression Using MultipleReference Depth Image-Based Rendering”, the disclosure of which isincorporated herein by reference. In the case of both light field 1.0and light field 2.0 the same arguments are valid.

With reference back to FIG. 4, decoding stage 450 operates in reverseorder and includes image/video decoder 421 and MR-DIBR decoder 425. Asshown, image/video decoder 421 (e.g., JPEG, JPEG 2000, or JPEG XSdecoder, or MPEG, H.264, HEVC, Theora, RealVideo, RV40, VP9, AV1, AVI,FLV, RealMedia, Ogg, QuickTime, or Matroska decoder) receives anddecodes the selected encoded reference views, reference disparity maps,and synthesized residuals provided by reference selection 410 togenerate decoded reference views 422, decoded reference disparity maps423, and decoded synthesized residuals 424 associated with one or moreselected RoIs. For example, image/video decoder 421 may include multiplevideo decoders (e.g., JPEG 2000 decoders) to decode the selected encodedreference views, reference disparity maps, and synthesized residuals.Reference views 422 and reference disparity maps 423 are provided toMR-DIBR decoder 425 for further decompression. MR-DIBR decoder 425decompresses reference views 422 and reference disparity maps 423 so asto generate synthesized views 426. Synthesized views 426 may besubtracted, by subtractor 412, from input light field data 402 to obtainsynthesized residuals 407. Synthesized views 426 may be added, by adder428, to synthesized residuals 424 to obtain decoded light field data427, which may be modulated (or displayed) on a light field displaydevice (e.g., light field display device 111 of FIG. 1).

FIG. 10 is a block diagram of a data processing system, which may beused with one embodiment of the invention. For example, the system 1500may be used as part of capturing system 103, light field display system107 and/or light field display device 111 as shown in FIG. 1. Note thatwhile FIG. 10 illustrates various components of a computer system, it isnot intended to represent any particular architecture or manner ofinterconnecting the components, as such details are not germane to theinvention. It will also be appreciated that network computers, handheldcomputers, mobile devices (e.g., smartphones, tablets) and other dataprocessing systems which have fewer components or perhaps morecomponents may also be used with the invention.

As shown in FIG. 10, the system 1500, which is a form of a dataprocessing system, includes a bus or interconnect 1502 which is coupledto one or more microprocessors 1503 and a ROM 1507, a volatile RAM 1505,and a non-volatile memory 1506. The microprocessor 1503 is coupled tocache memory 1504. The bus 1502 interconnects these various componentstogether and also interconnects these components 1503, 1507, 1505, and1506 to a display controller and display device 1508, as well as toinput/output (I/O) devices 1510, which may be mice, keyboards, modems,network interfaces, printers, and other devices which are well-known inthe art.

Typically, the input/output devices 1510 are coupled to the systemthrough input/output controllers 1509. The volatile RAM 1505 istypically implemented as dynamic RAM (DRAM) which requires powercontinuously in order to refresh or maintain the data in the memory. Thenon-volatile memory 1506 is typically a magnetic hard drive, a magneticoptical drive, an optical drive, or a DVD RAM or other type of memorysystem which maintains data even after power is removed from the system.Typically, the non-volatile memory will also be a random access memory,although this is not required.

While FIG. 10 shows that the non-volatile memory is a local devicecoupled directly to the rest of the components in the data processingsystem, a non-volatile memory that is remote from the system may beutilized, such as, a network storage device which is coupled to the dataprocessing system through a network interface such as a modem orEthernet interface. The bus 1502 may include one or more buses connectedto each other through various bridges, controllers, and/or adapters, asis well-known in the art. In one embodiment, the I/O controller 1509includes a Universal Serial Bus (USB) adapter for controlling USBperipherals. Alternatively, I/O controller 1509 may include an IEEE-1394adapter, also known as FireWire adapter, for controlling FireWiredevices.

The processes or methods depicted in the preceding figures may beperformed by processing logic that comprises hardware (e.g. circuitry,dedicated logic, etc.), software (e.g., embodied on a non-transitorycomputer readable medium), or a combination of both. Although theprocesses or methods are described above in terms of some sequentialoperations, it should be appreciated that some of the operationsdescribed may be performed in a different order. Moreover, someoperations may be performed in parallel rather than sequentially.

Embodiments of the present invention are not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof embodiments of the invention as described herein.

In the foregoing specification, embodiments of the invention have beendescribed with reference to specific exemplary embodiments thereof. Itwill be evident that various modifications may be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the following claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

What is claimed is:
 1. A computer-implemented method of light fieldimage encoding, comprising: receiving scene metadata and input lightfield images associated with a scene; performing a first encodingoperation on the scene metadata and the input light field images togenerate reference views and reference disparity information; performinga second encoding operation based on the reference views, the referencedisparity information, and synthesized residuals to output encoded lightfield data, wherein the encoded light field data comprises encodedreference views, encoded reference disparity information, and encodedsynthesized residuals; randomly accessing and selecting a group ofreference views and corresponding disparity information from the encodedlight field data based on one or more selected regions of interest; andtransmitting the selected group of reference views, the selectedcorresponding disparity information, and the encoded synthesizedresiduals.
 2. The method of claim 1, wherein randomly accessing andselecting the group of reference views and corresponding disparityinformation from the encoded light field data comprises: determining andselecting a first subgroup of reference views required for accessing afirst region of interest, wherein each reference view in the firstsubgroup has a closest in view distance to the first region of interest.3. The method of claim 2, wherein randomly accessing and selecting thegroup of reference views and corresponding disparity information fromthe encoded light field data further comprises: accessing additionalviews using the first subgroup of reference views.
 4. The method ofclaim 2, wherein randomly accessing and selecting the group of referenceviews and corresponding disparity information from the encoded lightfield data further comprises: determining and selecting a secondsubgroup of reference views required for accessing a second region ofinterest, wherein each reference view in the second subgroup has aclosest in view distance to the second region of interest.
 5. The methodof claim 4, wherein randomly accessing and selecting the group ofreference views and corresponding disparity information from the encodedlight field data further comprises: accessing additional views using thesecond subgroup of reference views.
 6. The method of claim 4, whereinthe second subgroup has fewer reference views than the first subgroup.7. The method of claim 4, wherein the first and second regions ofinterest are adjacent or non-adjacent regions of interest.
 8. The methodof claim 1, wherein the one or more regions of interest are selected bya user.
 9. The method of claim 1, wherein the one or more regions ofinterest comprise one view or a plurality of views.
 10. The method ofclaim 1, wherein the first encoding operation is a multiple-referencedepth image-based rendering (MR-DIBR) operation.
 11. The method of claim1, wherein the second encoding operation is a JPEG 2000 operation. 12.The method of claim 1, wherein the synthesized residuals are calculatedby subtracting synthesized views from the input light field images. 13.The method of claim 1, wherein the input light field images areelemental images or hogel images.
 14. A computer-implemented method oflight field image decoding, comprising: receiving a selected group ofreference views, selected corresponding disparity information, andencoded synthesized residuals associated with one or more regions ofinterest; performing a first decoding operation on the selected group ofreference views, the selected corresponding disparity information, andthe encoded synthesized residuals to output decoded reference views,decoded disparity information, and decoded synthesized residuals;performing a second decoded operation on the decoded reference views andthe decoded disparity information to generate synthesized views; andgenerating decoded light field data based on the synthesized views andthe decoded synthesized residuals.
 15. The method of claim 14, whereinperforming the second decoded operation comprises: forward warping eachreference disparity from the decoded reference disparity information toproduce a plurality of forward warped reference disparities, filteringeach of the forward warped reference disparities to generate a pluralityof filtered reference disparities, merging the plurality of filteredreference disparities into a merged disparity, and backward warping,using the merged disparity and the decoded reference views, to producethe synthesized views.
 16. The method of claim 14, wherein the receivedselected group of reference views and selected corresponding disparityinformation are produced by random access and selection of a set ofreference views and corresponding disparity information from encodedlight field data, the encoded light field data comprising encodedreference views, encoded reference disparity information, and encodedsynthesized residuals.
 17. The method of claim 16, wherein the randomaccess and selection of the set of reference views and correspondingdisparity information includes a determination and selection of a firstsubset of reference views required for accessing a first region ofinterest, wherein each reference view in the first subset has a closestin view distance to the first region of interest.
 18. The method ofclaim 17, wherein the random access and selection of the set ofreference views and corresponding disparity information further includesa determination and selection of a second subset of reference viewsrequired for accessing a second region of interest, wherein eachreference view in the second subset has a closest in view distance tothe second region of interest.
 19. The method of claim 17, wherein therandom access and selection of the set of reference views andcorresponding disparity information further includes an access ofadditional views using the first subset of reference views.
 20. Themethod of claim 18, wherein the random access and selection of the setof reference views and corresponding disparity information furtherincludes an access of additional views using the second subset ofreference views.
 21. The method of claim 14, wherein generating thedecoded light field data comprises adding the decoded synthesizedresiduals to the synthesized views.
 22. The method of claim 14, whereinthe synthesized residuals are calculated based on input light field dataand the synthesized views.